Not that I ever like defending Emma but her sister did just kill Synch (and attempted to kill more) and the Hellfire deaths were before she was rehabilitated. No matter what her thoughts were on Xavier, she likely had some degree of respect for him as the "father" of mutantkind.

I agree that the lupine thing is stupid
But making them related isn't the answer to me
It always felt forced that they tried to make them family.
If they stuck with the original, sabertooth-is-wolvie's-father thing from back in the day, it coulda worked. But its too late now, they're just rivals, not related.